There exists a great variety of optical sights of different types, in particular for installation on hunting, combat, or training weapons. In general a sight is utilized for aiming a weapon during daytime operation at a directly visible target and during nighttime operation at a target, which is only visible through the use of some vision-aiding devices.
Daytime sight devices range from simple front and rear sights like those on ordinary rifles to complex optical systems in combination with laser range finders and laser aiming devices. Certain sophisticated types such as telescopes are utilized to magnify a target and to enable the user during normal daytime operation to view a magnification of the target area at which the viewer is aiming.
There are also nighttime vision devices or sights, which employ image intensifiers or similar structures. The function of an image intensifier is to multiply the amount of incident light received to produce a signal that is bright enough for presentation to the eyes of a viewer. As such, these devices have been employed by the military and in commercial products as well. Sights vary in size, magnification, type of reticle, weapon application and level of performance.
An image intensifier tube (IIT) is a vacuum photoelectronic device intended either for transformation of an invisible IR, UV, or X-ray image of an object into a visible image or for intensification of a visible image. An IIT normally consists of a photocathode, an image intensification system, and a cathode-luminescent screen. The photocathode transforms the original optical image into a so-called electronic image. With the use of the image-intensifying system, the electronic image is transferred to the screen where this image, in turn, is converted into a visible original image. In the IIT, the light reflected from the object causes emission of electrons (photocurrent) from the surface of the photocathode. In this case, a magnitude of photocurrent generated by various areas of the photocathode depends on distribution of density of images projected onto these areas. Photoelectrons accelerated and focused by the IIT's field bombard the screen, thus causing it to luminesce. Since brightness on individual areas of the screen depends on density of the photocurrent, the screen reproduces a visible image of the object.
There exists a great variety of IIT's that have different constructions, methods of attachment to the weapon, and principles of use and operation.
Since it is advantageous to use the same weapon with daytime and nighttime vision devices, many contemporary weapons are provided with possibility of installing both daytime and nighttime sights.
For example, U.S. Pat. No. 4,822,994 discloses a configuration in which the front end of a telescopic sight is separable from the rest of the sight. For nighttime use an image-intensifier module is inserted between the sections. However, for daytime operation, the user must disassemble the sight and remove and store the image-intensifier module.
One disadvantage to having separate daytime and nighttime sights is that the sights must be individually boresighted to the weapon whenever the sight is initially installed, and must be checked for boresight whenever the sight is reinstalled on the weapon. Current use of weapon sights by law enforcement and military personnel and by civilian users involves the careful mounting and boresighting of a day and/or night vision sight to the weapon. For maximum accuracy, actual firing of the weapon is required during the boresighting process. This is not generally feasible under combat conditions. Separate weapon sights are also disadvantageous because the sights must be interchanged for day or night use. In addition, the separate night vision sight adds an additional three to four pounds, which must be carried and handled separately by the user.
On the other hand, it is understood that the lenses of the objective lens unit and of the ocular lens unit may form a conventional optical daytime sight, which comprises a conventional telescopic tube with adjustable magnification. It is obvious that such daytime conventional telescopic sight can be combined with a night vision device such as IIT to form a self-contained device, and a great variety of optical sight systems which can at the same time be used both in daytime and nighttime merely by switching and without disconnection have recently appeared on the market and became a subject of new patents.
For example, U.S. Pat. No. 5,084,780 issued in 1992 to E. Phillips and U.S. Pat. No. 5,946,132 issued to the same inventor in 1999 disclose a telescopic sight that can be used for either nighttime or daytime operation and is particularly adaptable for use on weapons ranging from rifles to anti-tank weapons. A first embodiment includes a single objective and two parallel light paths, one for day viewing and one for night viewing. The objective forms the beginning of the night path. Separating dichroic mirrors transmit light from the objective along the night path and reflect light from the objective to the day path. The night path includes an IIT. A mirror at the end of the night path reflects the light from the IIT to a beamsplitter/combiner on the day path. The beamsplitter/combiner transmits the light from the day path and reflects the light from the night path along the same path to an ocular assembly for viewing. A second embodiment of the telescopic sight is similar to the first embodiment but contains two objective lens assemblies for collecting light, one for the night path and one for the day path. Because the sight has two separate objective lens assemblies, separating mirrors are not included. A third embodiment includes a projected aiming reticle and a direct view capability for day viewing which replaces one of the objective lens assemblies. The direct view channel includes a beamsplitter/combiner.
Furthermore, both patents of Phillips describe various methods for introducing an image of a reticle to the combined day and night optical path.
In spite of all advantages of the aforementioned optical sight system, it utilizes two parallel optical paths always used simultaneously irrespective of nighttime or daytime application. It is obvious that the use of two separate optical paths at the same time makes the sight optics large and heavy, which is a significant drawback for weapons, which are manually carried by the user.
The device based on the same principle of simultaneous and constant use of daytime and nighttime optical paths is disclosed in another U.S. Pat. No. 5,902,996 issued in 1999 to K. Sauter. This device is provided with two rotating mirrors, which can be rotated simultaneously for opening or closing the night vision system. Although this system is more reliable than the previous one, in general it entails the same disadvantages since it does not suggest any other new solutions of the problems inherent in the sight with two parallel and simultaneously working optical paths.
The above problem is solved by the system described in U.S. Pat. No. 6,131,294 issued in 2000 to U. Jibiki. This device comprises a telescopic sight with a small, separate night-vision block insertable into the daytime optical path between the ocular lens and the objective lens. A special recess is formed in the sight housing for fitting the insertable block into this recess with alignment of the optical path of the night-vision insert with that of the daytime sight portion. Insertion is carried out without the use of any special instruments or fasteners.
Although the U.S. Pat. No. 6,131,294 solves the problems of the earlier described devices by providing a single-path day/night vision optics, it is still possesses a number of significant disadvantages, which are the following.
Disconnection of the night-vision device, such as the image intensifier, exposes two optical surfaces on the opposite sides of the recess. During the use of the sight in the daytime mode these optical surfaces remain unprotected. Penetration of scattered day light into the aforementioned recess contributes to decrease in contrast of the image. Furthermore, the night-vision device, such as an image intensifier tube, is a very delicate optical instrument, which requires accurate handling after replacement. Therefore the use of the device of U.S. Pat. No. 6,131,294 is unsuitable for combat field conditions.
When the night-vision insert has a temperature different from the temperature of the stationary part of the sight, insertion of the night-vision block may cause fogging of the sight optics, which can make the sight inoperative for a substantial period of time.
Another problem associated with the use of the insertable night-vision block consists in that each insertion and removal requires readjustment of the optical system for refocusing.
U.S. Pat. No. 4,961,278 issued in 1990 to Ch. Johnson, et al., describes a sight apparatus for selective daytime and nighttime use due to provision of a rotating housing located between the ocular and objective of the telescopic sight assembly. This housing contains an image-intensifier unit for nighttime use and a lens coupling assembly for daytime use which are rigidly attached to opposite arms of a two-arm lever so that rotation of this level by about 180° will alternatingly align the optical axis of the sight either with the image-intensifier unit or with the daytime lens coupling assembly which is placed in the optical path of the sight. A disadvantage of this device consists in that in addition to an image-intensifier unit it requires the use of an auxiliary daytime coupling assembly, both of which must be attached to opposite arms of a pivotable lever. The use of the auxiliary daytime coupling contributes to an increase in the weight of the sight. Furthermore, as the coupling assembly and the image intensifier have diametrically opposite positions and the lever that supports these units has to be rotated by 180° in order to have enough room for such rotation the sight should have increased overall dimensions. Moreover, switching between the daytime optics and nighttime optics requires manual focusing and magnification with the use of a focusing and magnification mechanism. Another disadvantage of the design described in the aforementioned patent is that switching between the daytime use and the nighttime use requires rotation of the aforementioned lever with the entire housing and with switchable optics respective to the sight housing. This means that the housing of the sight consists of two separate parts, one of which is rotatingly installed on the other. Another essential disadvantage of the sight disclosed by the aforementioned patent consists of the arrangement of rotatable optics for rotation in a plane perpendicular to the optical axis of the sight. Such an arrangement contributes to an additional and significant increase in the sight dimensions because for efficient operation the image intensifier requires a high aperture ratio and this, in turn, requires the use of electrooptics of large diameter. This leads to an increase in the vertical dimension of the sight.
The problems of the above patent are solved in a self-contained day/night optical sight disclosed in U.S. Pat. No. 6,608,298 issued in 2003 to Leonid Gaber, who is an applicant of the present patent application. The apparatus is comprised of a telescopic sight assembly unit having a pivotable housing section located between the ocular and objective of the telescopic sight assembly. The aforementioned housing section contains an image intensifier tube for nighttime use and a mechanism coupled to the aforementioned housing section for pivoting it between a first and second positions indicative of a daytime and a nighttime mode, whereby when installed in the second position, the image intensifier tube is aligned with the optical axis of the telescope to provide nighttime operation and where it is installed in the first position, the image intensifier tube is removed from the optical axis to provide daytime operation.
A disadvantage of such an apparatus is that it is self-contained with the built-in image intensifier tube. This means that the image intensifier tube cannot be separated and removed from the sight, e.g., for replacement with another image intensifier tube or an optical device of another type. In other words, when a telescopic part or IIT requires maintenance or replacement, the entire apparatus has to be replaced.
Nevertheless, all day/night sights for weapons described above and those known to the applicant, including those that contain removable IIT's or IIT's switchable between the operative and inoperative positions, have complicated and relatively expensive construction and significant weight and are not universal in the sense that in the majority of cases they are bound to weapons of specific models.
For the solution of the problems inherent in the prior art technique, Tactic Solutions, LLC of Nevada, USA has developed a universal IIT known as Model PVS-14 Series Monoloc on the Leupold M1 Long Range Optics attachable to the rear side of a tubular sight optics so that the image intensifier tube is located between the viewer's eye and the ocular of the tubular sight (see http:monoloc.com/main.php?id_page=72).
In spite of the fact that this device is not of the type permanently installed together with the tubular optics and is not switchable between operative and inoperative positions, it is advantageous in that it is extremely light in weight, small in size, and, most importantly, quickly and easily attachable to rifle scopes of many models of military and hunting rifles, digital cameras, camcorders, Close Quarters Battle (COB) optics, and laser rangefinders, or spotting scopes, for night and reduced-ambient lighting conditions.
Although these advantages to some extent compensate for the necessity of frequent attaching/detaching operations, a serious disadvantage of the universal IIT of the above type is that it must be installed between the viewer eye and the ocular of the tubular optics, and this changes the eye-relief distance. Eye relief is the distance from the observer's cornea to the nearest optical surface of the eyepiece; this is the distance at which the entire (or largest) field of view is visible. In other words, the IIT attached to the rear end of the conventional tubular optics significantly shortens the eye-relief distance to the extent that in some cases the recoil at the moment of shooting hits the user between the eyes. In order to eliminate this problem, the user has to move the eye further away from the IIT's ocular, and in this case he/she cannot see the entire field of observation, and shooting conditions become inconvenient. This is shown in FIGS. 1 and 2, where FIG. 1 is a view of a conventional daytime tubular optical sight 20 with the eye relief H1 that corresponds to use of the sight 20 without an IIT, and FIG. 2 is a view of the tubular optical sight 20 with the eye relief H2 that corresponds to use of the sight 20 when the IIT 22 is attached to the rear end of the optical sight 20. Reference numeral 24 designates a viewer's eye. It can be seen that with the IIT 22 attached to the optical sight 20, the eye relief H2 becomes significantly shorter than the eye relief H1 required for normal shooting. Therefore, the user has to move the weapon forward and cannot have normal conditions under which the weapon can rest on the user's shoulder.
The problems experienced by a shooter in using a rearwardly attached night scope are well described By Craig Boddington in his articles at http://www.gunsandammomag.com/gun_columns/relief—1021/.